Electrically operated, handheld devices are commonly used today in various medical and dental procedures. These devices may be used, for example, to rotate burrs, drills, and dental files for cutting away or shaping different types of tissue. Typically, these devices include an electronic controller, a variable speed handheld motor, and a gear head. The controller is electrically connected to the motor and can vary the power to the motor thus varying the motor output speed. The gear head includes an output which is connected to the desired tool for rotating the tool at a predetermined speed. Gear heads are generally available in many different input/output speed ratios and a selected gear head is typically connected to the motor both to provide a mechanical connection to the desired tool and to step-up or step-down the rotational speed of the tool relative to the speed of the motor.
A significant problem with existing handheld instruments of this type is that the motors are usually limited to a small range of output speeds. A typical output speed of handheld instruments is approximately 1,000 rpm to 20,000 rpm. Tool rotation requirements, however, can often vary between 250 rpm and 200,000 rpm depending on the medical or dental procedure. For example, root canal files need to be rotated at relatively slow speeds of between about 250 rpm and about 500 rpm. Dental drills may be rotated in a range of about 2,000 rpm to about 4,000 rpm. Diamond burrs, for example, used for cleaning, shaping or polishing work in the dental field ideally rotate at relatively high speeds. These speeds may reach 150,000 rpm to 200,000 rpm or above. To achieve a wide range of different speeds, given the relatively limited speed range of a motor, different gear heads are purchased by end users to step-up (i.e., multiply) or step-down (i.e., reduce) the final output speed of the instrument or tool according to the needs of the user. This typically requires the purchase of a number of different, and expensive, gear heads. In addition, the output speed displayed on the motor controller typically relates only to the motor output and thus the actual final tool speed must be separately calculated by the user depending upon the specific gear ratio of the chosen gear head. These calculations can be error-prone.
In view of these and other problems in the art, it would be desirable to provide a medical and/or dental instrument for rotating a tool that can reduce or eliminate the need for several different gear heads to perform a number of different medical or dental procedures.